Chronograph Accuracy Tips

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trazman
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Chronograph Accuracy Tips

Postby trazman » Thu Apr 16, 2015 6:17 am

I had some hard time yesterday on the range with my chrono, so I searched the internet and fount a nice article about Chronograph Accuracy Tips on Precision Rifle Blog:

1.You’ll get the best readings with even lighting. Best case scenario is overcast skies, and worse is direct sunlight on the skyscreens.
2.Remove diffusers in overcast or shaded conditions. The diffusers are only necessary in sunny conditions, and by removing them in other conditions you’ll allow more light into the chronograph.
3.On sunny days place the chronograph in the shadow of a building or opaque wall. Ensure the sensors have a clear view of the sky, but the chronograph itself is in the shade. You could alternatively add sun shields to create a shadow (see Advanced Techniques section for more details). The goal is to eliminate direct sunlight on the chronograph, while still ensuring the sensors have a direct view of the sky. However, avoid placing the chronograph in the shade of a tree. The uneven, dappled sunlight that filters through the tree will cause more problems than it will solve.
4.Avoid low light conditions, such sunrise and sunset. During those times the extreme low angle of the sun can cause additional issues due to reflections.
5.Clean skyscreens. If you’ve used your chronograph more than a dozen times, there is likely a build-up of dust on the sensors. Use a Q-tip or canned air to clean the lenses, being especially careful not to scratch them.
6.Ensure chronograph is level
7.Ensure sensors aren’t tilted. If using a Shooting Chrony, ensure it is completely unfolded. This would result in a similar margin of error as the example above, because the real distance the bullet traveled doesn’t match what the chronograph is assuming it did. But in this example, the reading would actually be around 4% faster than the bullet was really travelling.
8.Position the chronograph 15-20’ from the muzzle to avoid interference from muzzle blast. To get true velocity at the muzzle (what most ballistics programs need), you can typically add .75 mph per foot. For example, if the chronograph was 20’ from the muzzle and displayed a reading of 3,200 fps you would just add on 20*.75, which is 15. So your true muzzle velocity would be 3,215 fps.
9.Paint all surfaces flat black to avoid erroneous readings caused by reflections, including all chronograph and tripod surfaces that would be in direct line of sight with the bullet as it passed over the chronograph.
10.Use a quality tripod for a stable platform.
11.Avoid shooting over reflective surfaces like snow or some types of sand. May be able to reduce reflection by laying out a large, dark colored tarp under the chronograph setup.
12.Replace batteries regularly to ensure stable power.
13.Understand the flight of your bullet will be lower than your sight picture. Most scopes are mounted 1.5” higher than the centerline of the barrel. Always aim much higher than the middle of the shooting area.
14.Avoid using near florescent lamps. Although we can’t detect it with our naked eye, they actually vary in intensity many times a second and chronographs will detect these changes rendering them virtually useless.
15.To work indoors, chronographs need a lot of even lighting … which is hard to pull off with incandescent lamps. A white background with even amounts of light over the sensing area works best. Some chronographs offer optional accessories that help make them more reliable indoors.

You can find the original article here:
http://precisionrifleblog.com/2012/07/2 ... liability/

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Deerhunter338mag
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Re: Chronograph Accuracy Tips

Postby Deerhunter338mag » Fri Apr 17, 2015 10:11 am

I found to fire 5 shots and give about 7 minutes between each shot to give equal chance to each shot. I then add them all up and divided it by 5 to get the average speed then I validate at various ranges to get the Speed spot on. Or buy a magnetospeed :D
Aim small, miss small

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squeek
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Re: Chronograph Accuracy Tips

Postby squeek » Sat Apr 18, 2015 8:50 am

I'm using a magnetospeed 2, no hassle with light and on some ranges over here they will not allow you to get beyond the bench to set up your equipment. A magnetospeed is attached to the barrel so no problem even for the most small minded safety officer.

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Deerhunter338mag
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Re: Chronograph Accuracy Tips

Postby Deerhunter338mag » Tue Apr 21, 2015 11:01 am

Yep magnetospeed are the go I think. Well worth the extra bit of coin you pay for them.
Aim small, miss small

trazman
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Re: Chronograph Accuracy Tips

Postby trazman » Tue Apr 21, 2015 1:45 pm

What about accuracy and POI with and without magnetospeed? Is it possible to do load developement with it?

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squeek
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Re: Chronograph Accuracy Tips

Postby squeek » Tue Apr 21, 2015 7:34 pm

A couple of dutch military guys tested poi shift with and without (real) bajonets on their rifles and they found no shift in poi so i expect the much lighter plastic 'bajonet' from the magnetospeed doesn't influence noticably

RVargueS
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Re: Chronograph Accuracy Tips

Postby RVargueS » Wed Apr 22, 2015 11:30 pm

Hi,
I have heard that the magnetospeed makes a shift in POI because it changes the barrel harmonics, and its only for velocities.

I don't know if this is so, but it makes sense.

Lrhunter
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Re: Chronograph Accuracy Tips

Postby Lrhunter » Wed May 20, 2015 6:18 am

I am still deciding on which crono to get... I am also looking at Super Crony, but some people like it and some not... Hard to decide...

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Deerhunter338mag
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Re: Chronograph Accuracy Tips

Postby Deerhunter338mag » Wed May 20, 2015 1:21 pm

I found it made no difference with magnetospeed poi still shot fine
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dchamp
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Re: Chronograph Accuracy Tips

Postby dchamp » Wed May 20, 2015 3:30 pm

I recently purchased a Magneto Speed and have used it only once so far. I was happy with the results. My son mounted it on his AR and shot it prone along with his Pro Chrono at 15ft away. Then I fired off the bench two different rifles with the Magneto Speed and through an Oehler 35 at 11’-6 away. All shots from the Magneto Speed were consistently 23-25fps faster. This was good to know and the consistency gave us confidence in the Magneto Speed.

As to the POI shift I have no experience but, my friend (a retired engineer) who is very good with load development and accuracy told me he has experienced POI shifts and has seen the barrel walk during load development with the Magneto Speed attached to his barrel.
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